What Is an ASN? Autonomous Systems and Who Runs the Internet

Check your IP on our homepage and you'll see an ASN field — something like AS15169 next to your provider's name. That number places you within the internet's true structure: not one network, but roughly a hundred thousand independent networks stitched together. Each is an autonomous system.

What an autonomous system is

An AS is a network under one administrative roof with its own routing policy — an ISP, a cloud provider, a university, a big enterprise. Each is identified by a globally unique number assigned through the same registries that allocate IP blocks (WHOIS shows the mapping). Famous examples: AS15169 (Google), AS13335 (Cloudflare), AS32934 (Meta). Your ISP has one too — it's the "org" attached to your address.

How ASNs run the internet: BGP

Autonomous systems announce to each other which IP ranges they can deliver, using the Border Gateway Protocol (BGP). "AS64500 here — I can reach 203.0.113.0/24." Neighbouring networks propagate these announcements, and every router on the backbone assembles a map of which AS-path leads to every block. When you load a website, your packets hop from your ISP's AS through perhaps two or three others to the destination's AS — visible as the network names in a traceroute.

Why BGP trust matters

BGP was designed among networks that trusted each other, and it shows. A network that wrongly announces someone else's ranges — a BGP hijack or more often an innocent "route leak" — can vacuum up traffic meant for others. Famous incidents have taken major services offline for hours. Defences like RPKI (cryptographically signed route ownership) are steadily closing the gap, but the episode explains why "the internet routed around it" and "the internet broke" are both BGP stories.

What your ASN reveals about you

• Your real provider — resellers ride on someone's AS; the ASN names the actual network.
• Connection type — residential ISP ASNs vs datacenter/cloud ASNs vs mobile carriers. Fraud and anti-bot systems weigh this heavily: traffic from a hosting ASN gets far more suspicion than a residential one.
• VPN detection — connect a VPN and your visible ASN switches to the VPN's hosting provider, which is precisely how many services notice.

ASN, IP block, geolocation and reverse DNS together form the standard toolkit for answering "who and what is behind this address."

Frequently asked questions